Coronary atherosclerosis will be studied in a model (cynomolgus monkeys) in which certain features that characterize the disease in man will have been induced. Previous experience indicates that after 0.1 percent cholesterol has been added to a semipurified diet, plasma cholesterol levels of 300 to 500 mg/100 ml can be obtained in these monkeys and atherosclerotic lesions develop in the main branches of the coronary arteries. After atherosclerosis has been established, drugs prescribed for the treatment of human hypercholesterolemia will be added to the diets to determine whether they (1) arrest the progression or (2) induce regression of the disease. The effects of cholesterol feeding and drug therapy on ventricular excitability and on the threshold for ventricular fibrillation will also be determined. In addition, the effects of drug therapy on plasma lipoprotein levels, aortic and carotid atherosclerosis, arterial structure, and liver and kidney function and pathology will be studied.